package com.seeyon.kk.modules.ibatis.dialect;

/**
 * @author badqiu
 */
public class DB2Dialect extends Dialect {

	@Override
	public boolean supportsLimit() {
		return true;
	}

	@Override
	public boolean supportsLimitOffset() {
		return true;
	}

	private static String getRowNumber(String sql) {
		StringBuffer rownumber = new StringBuffer(50).append("rownumber() over(");

		int orderByIndex = sql.toLowerCase().indexOf("order by");

		if (orderByIndex > 0 && !hasDistinct(sql)) {
			rownumber.append(sql.substring(orderByIndex));
		}

		rownumber.append(") as rownumber_,");

		return rownumber.toString();
	}

	private static boolean hasDistinct(String sql) {
		return sql.toLowerCase().indexOf("select distinct") >= 0;
	}

	@Override
	public String getLimitString(String sql, int offset, String offsetPlaceholder, int limit, String limitPlaceholder) {
		int startOfSelect = sql.toLowerCase().indexOf("select");

		StringBuffer pagingSelect = new StringBuffer(sql.length() + 100).append(sql.substring(0, startOfSelect)) //add the comment
				.append("select * from ( select ") //nest the main query in an outer select
				.append(getRowNumber(sql)); //add the rownnumber bit into the outer query select list

		if (hasDistinct(sql)) {
			pagingSelect.append(" row_.* from ( ") //add another (inner) nested select
					.append(sql.substring(startOfSelect)) //add the main query
					.append(" ) as row_"); //close off the inner nested select
		} else {
			pagingSelect.append(sql.substring(startOfSelect + 6)); //add the main query
		}

		pagingSelect.append(" ) as temp_ where rownumber_ ");

		//add the restriction to the outer select
		if (offset > 0) {
			//			int end = offset + limit;
			String endString = offsetPlaceholder + "+" + limitPlaceholder;
			pagingSelect.append("between " + offsetPlaceholder + "+1 and " + endString);
		} else {
			pagingSelect.append("<= " + limitPlaceholder);
		}

		return pagingSelect.toString();
	}
}
